1. Field of the Invention
The present invention relates to lead-free soldering technology electronics, and more particularly to a tin whisker mitigation material using thin film metallic glass underlayer.
2. Description of the Prior Art
Currently, electronics packaging technology mainly uses copper or iron-nickel alloy as a conductive lead frame for electrically connecting chips and printed circuit board (PCB). However, because both the copper lead frame and the iron-nickel lead frame cannot join with the PCB well, a solder-plating layer is coated on the surface of the lead frame for enhancing the connection of the lead frame and the PCB.
The solder-plating layer is traditionally made of tin-lead alloy, and has been replaced by lead-free solder because the lead (Pb) is an unrecyclable toxic material. However, lead-free solder would spontaneously produce tin whisker under room temperature; moreover, when the tin whisker is produced to include a specific length, the tin whisker may connect to the two adjacent solder pins in a packaged electronic component, and then causes the two adjacent solder pins to short. Besides, when the length of the produced tin whisker is almost equal to the space of the two adjacent solder pins, the point discharge may occur and produce spark to fail the packaged electronic component.
Accordingly, a method for inhibiting the growth of tin whisker is proposed. Referring to FIG. 1, which illustrates a flow chart of a conventional method for inhibiting the growth of tin whisker; moreover, please simultaneously refer to FIG. 2, there is shown a side cross-sectional view of a multi-layer structure fabricated by using the method. The method for inhibiting the growth of tin whisker mainly includes 3 steps.
As shown in FIG. 1 and FIG. 2, the method is firstly proceeded to step (S01′), providing an iron-nickel alloy substrate 202′, wherein the weight percent of the nickel in the iron-nickel alloy substrate 202′ is ranged from 42 wt % to 60 wt %. Next, the step (S02′) is executed for forming a nickel layer 204′ on the surface of the iron-nickel alloy substrate 202′, and the thickness of the nickel layer 204′ is ranged from 1 μm to 2 μm. Finally, the method is proceeded to step (S03′), forming a tin layer 206′ on the nickel layer 204′, and the thickness of the tin layer 206′ is ranged from 3 μm to 20 μm. Thus, the stress in the internal of the tin layer 206′ can be prevented by the nickel layer 204′, therefore the growth of tin whisker would be further inhibit, so as to prevent the tin whisker growing on the surface of the tin layer 206′.
The above-mentioned method can indeed effectively inhibit the growth of tin whisker by way of forming an electroplated nickel layer 204′ with the thickness of 3 μm-20 μm as an underlayer between the Cu/Sn interface. However, it needs to further concern the issues brought by the above-mentioned method are that: (1) the waste produced by the electroplating process is harmful to environment; and (2) the 20 μm electroplated nickel layer 204′ would increase the manufacturing method of the electronics package.
Thus, through above descriptions, it is able to know that conventional method for inhibiting the growth of tin whisker still includes drawbacks and shortcomings, so that the inventor of the present application has made great efforts to make inventive research thereon and eventually provided a tin whisker mitigation material using thin film metallic glass underlayer.